The invention is related to storage systems and in particular to migration in a allocation as needed (i.e., thin provisioned) storage system.
Allocation-on-use (allocation-as-needed, also referred to as “thin provisioning”) technology provides an efficient storage space management for virtual volumes, since space is allocated on an as-needed basis. Conventional “manual provisioning” of storage involves installing the actual physical storage called for; e.g., if 10 terabytes (TB) of storage is required, then in a “manual provisioning” approach, 10 TB of storage is purchased and installed. Manually provisioned volumes are referred to herein as “normal volumes”. Thin provisioning allows a user (e.g., administrator) to create volumes of any size without actually purchasing or installing the entire amount of disk storage. Thin provisioned volumes are referred herein as “thin provisioned volumes.” A common use of thin provisioning is in virtual storage systems, where “virtual volumes” in the virtual storage are provided as thin provisioned volumes. Commonly owned U.S. Pat. No. 6,725,328 shows an example of thin provisioning, referred to therein as allocation-on-use.
Current data migration technologies for volumes such as Logical Units (LUs) in the SCSI environment perform operations on a block-by-block basis irrespective of the data in the blocks. If we use the current migration technology for thin-provisioning technology, the benefits of thin provisioning will be lost because conventional migration technology copies all blocks in the source volume to the target volume. Consequently, even in a thin-provisioning system, all blocks would be allocated. Improvements in this area of storage technologies can be made.
As the amount of information treated in a computer system for use in companies, corporations, etc. is drastically increased, the capacity of a storage device such as a disk for storage of data has been increased steadily in these years. For example, a magnetic disk storage system having a capacity of the order of terabytes is very common. With respect to such a disk storage system, there is a technique by which a single storage device subsystem is made up of a plurality of types of logical disks (which will be sometimes referred to merely as disks), e.g., as disclosed in U.S. Pat. No. 5,956,750, incorporated herein by reference. Disclosed in the disclosure is, more specifically, a disk subsystem which is made up of disks having different RAID levels such as RAID5 and RAID1 as devices (logical disks) to be accessed by a host computer, or made up of disks having different access rates as actual magnetic disks (physical disks) of logical disks. A user can selectively use the devices according to the access rates of the respective devices.